Heat assisted magnetic recording (HAMR) generally refers to the concept of locally heating a recording media to reduce the coercivity of the media so that an applied magnetic write field can more easily change the magnetization direction of the media during the temporary magnetic softening of the media caused by the heat source. A tightly confined, high power laser light spot is used to heat a portion of the recording media to substantially reduce the coercivity of the heated portion. Then the heated portion is subjected to a magnetic field that sets the direction of magnetization of the heated portion. In this manner the coercivity of the media at ambient temperature can be much higher than the coercivity during recording, thereby enabling stability of the recorded bits at much higher storage densities and with much smaller bit cells.
The principles of HAMR are based on i) choosing a medium with very high coercivity to ensure that the medium still satisfies the superparamagnetic limit with very small grain volumes, and ii) reducing the coercive field during the write process by heating the medium, for example, with a focused laser beam. When the magnetic medium is heated, the coercivity is reduced making writing possible. Then, after writing the bit, the medium cools back to its original temperature with high coercivity allowing the medium to be thermally stable.